1. Field of the Invention
The present invention relates to a reluctance type rotating machine equipped with permanent magnets, which is compact with a high output and which is capable of rotating in a wide range by its adoption of a new pole structure.
2. Description of the Related Art
As shown in FIG. 1, an earlier reluctance type rotating machine comprises a stator 1 having armature windings 2 and a salient-pole rotor 3 having an uneven core 4 since the rotating machine does not require coils for forming a field system about the rotor 3. Therefore, the reluctance type rotating machine is simple in structure and low in price, We now describe a principle of producing the output of the reluctance type rotating machine. Because of unevenness about the rotor, the reluctance type rotating machine exhibits small magnetic reluctance at protrusions of the rotor and large magnetic reluctance at recesses of the rotor. That is, there is a difference of stored magnetic energy between a gap over the protrusion and another gap over the recess. The output of the reluctance type rotating machine comes from the change in magnetic energy. Note, the protrusions and recesses may be provided by a configuration allowing the unevenness to be formed not only geometrically but magnetically, in other words, the configuration where the magnetic reluctance and distribution of magnetic flux density vary depending on the position of the rotor.
As another high-performance rotating machine, there is a permanent magnet type rotating machine. In the rotating machine, a plurality of permanent magnets are arranged on the substantial whole periphery of the rotor core although the armature windings of the machine is similar to the armature windings of an induction machine, the same windings of the reluctance type rotating machine, etc.
Due to the unevenness about the core surface, the reluctance type rotating machine has different magnetic reluctance which depends on the rotational position of the rotor. This change in magnetic reluctance causes the magnetic energy to be varied thereby to produce an output of the rotor.
In the conventional reluctance type rotating machine, however, the increasing of currents causes a local magnetic saturation to be enlarged at the protrusions of the rotor 4. Thus, the enlarged magnetic saturation also causes magnetic flux leaking to the recesses between poles to be increased, so that effective fluxes are decreased while lowering the output power.
On the other hand, as another high-powered rotating machine, there is a permanent magnet type rotating machine using "rare-earth metal" permanent magnets having high magnetic energy products. Owing to the arrangement of the permanent magnets on the surface of the rotor core, when the permanent magnets of high energy are employed to form a magnetic field, the permanent magnet type rotating machine is capable of forming an intense magnetic field in an air-gap of the machine, providing a compact and high-powered rotating machine.
Nevertheless, it should be noted that a voltage induced in the armature windings gets larger in proportional to the rotating speed of the rotor since the magnetic flux of each magnet is constant. Therefore, if the machine is required to operate at a wide range of variable speeds up to the high-speed rotation, it is difficult to carry out the "rated-output" operation of the machine at a rotating speed twice or more as large as the base speed under constant current and voltage.